Filtering plants of this type are known and described for instance in EP-B-0 428 862 and DE-A-195 27 311. The porous candle filters or filter elements are made for instance of ceramics, fibrous material or also from metal, they may be disposed for instance upright or pendent or in any other position and be connected with the associated clean gas passage. A filtering plant usually has several groups of filter elements, which groups are arranged one beside the other and/or above the other in a housing, where each group can be cleaned separately from the other groups. This requires valves, and it is important to early detect malfunctions of these valves, in order to avoid negative effects on the filter elements.